Respiratory syncytial virus (RSV) is the commonest cause of respiratory ailments in newborn infants: bronchopneumopathies (bronchiolitis). The WHO estimates that 50 million individuals are affected by RSV every year, of whom 160,000 die worldwide. There are two subgroups of the virus (subgroups A and B).
RSV is classified in the family Paramyxoviridae, genus Pneumovirus, containing an unsegmented RNA genome of negative polarity coding for 10 specific proteins.
No vaccine against RSV is currently available. Vaccines containing inactivated virus have been shown to be ineffective and have even sometimes aggravated the infections of newborn infants. In the 1960s, the attempts at vaccination with formalin-inactivated RSV led to failure: instead of conferring protection on reinfection due to RSV, the vaccine had the effect of aggravating the ailment in the child.
Application WO 87/04185 proposed the use of RSV structural proteins for the purpose of a vaccine, such as the envelope proteins known as F protein (fusion protein) or G protein, a 22-kD glycoprotein, a 9.5-kD protein or the major capsid protein (N protein).
Application WO 89/02935 describes the protective properties of the whole F protein of RSV, where appropriate modified in monomeric or deacetylated form.
A series of fragments of the F protein has been cloned for the purpose of investigating their neutralizing properties.
However, the immune vaccines tested hitherto have been shown to be ineffective or have induced a pulmonary pathology (bronchiolitis or peribronchitis).
At the present time, no treatment of primary choice exists for infections due to RSV.
RSV infections of the upper airways: treatment is based essentially on symptomatic medication identical to that used for other viral infections.
RSV infections of the lower airways: treatment in newborn infants is based on the maintenance of correct hydration, the suctioning of secretions and the administration of oxygen if necessary. A positive effect has been observed with ribavirin, a nucleotide which is active in vitro against RSV.
In order to facilitate the administration of the vaccine, it would be desirable to have at one's disposal a product which is active via the oral route, generating a good immunity with reduced side effects.